Dual sidedrafts

[DatDoug]

Put on my dual weber 40 DCOE sidedrafts on today and noticed there is nowhere to run the vaccum advance hose:confused: WTF? Just plug it off and run w/o? It runs idles good but when I get it out on the road and put my foot into it it bogs. Is this due to no Vacuum advance? Everything else is new. Rebuilt L20 with cam and electronic ignition.

[benzo]

someone correct me if I am wrong.

 

I would think you would have to drill and tap the manifold for a nipple to connect the vaccum advance as that distributor relies on it to perform well. If not you may have to use a dist like a single point with pertronix and have it recurved. I am running dual sidedrafts with the pertronix but I notice others who use sidedrafts with the matchbox dist hook up the vaccum advance. right now the motor may be loading up with fuel since the dual sides are adding more fuel and the dist is not firing off or timed correctly to burn off that feel giving that bogging situation.

[banzai510(hainz)]

My beater has 40mm mikunis. It has ONE port on the carb itself to the distributor.

My 44mm Mikunis on my yellow car has no port sand I dont run one. Seems to run fine and has a SSS dizzy with Pertronix. seems to run fine and dont notice a difference.

 

set advance up to 12-15 BTDC w/timming light and see how that runs.

 

I believe on my 40s my fuel jet is 135 mains 160 air on the jet block

 

 

Someone said I think you want the port vacuum in by the butterfly of the carb NOT in the inatke manifold tube. Might give a PULSATING instead of smooth vaccum.Since it from One clyinder

Edited June 14, 2009 by banzai510(hainz)

[DatDoug]

I spliced into the brake booster vacuum line and it made no difference. Runs and idles great but when under load (accelerating) it bogs. I have it advanced to 14 and run premium fuel. I guess I need to get the synchro tool and tinker with them more. I checked the plugs and they look normal.

[datsunfish]

You only want advance at acceleration. So never run it from the manifold or anywhere else with constant vacuum. It defeats the purpose. People like to say that you have no vacuum when the throttle is open but what you have is flow that pulls through the vacuum port as well as the carb chamber when you open the throttle plate.

Check everything closely for any vacuum leaks. You might not notice it until there is less flow through the carbs because all that vacuum is pulling air ahead of the carbs not through them.

A hesitation means lean and bogging or sluggishness will be too rich. Do the carbs have adjustments for the pump throw? Maybe set it for more immediate action and less at full throttle. If it has it. I think my mikunis do.

[banzai510(hainz)]

A hesitation means lean and bogging or sluggishness will be too rich. Do the carbs have adjustments for the pump throw?

 

Look into that one as I seen a so called rebuilt Mikuni set have the accel pump diapram in upside down. Hit the gas it would bog out unless you slowly increased gas then it ran fine like a SU.

Ck Pump lever as Datsunefish suggested.

 

 

maybe ck the carb jet block #s just to give us a indication of whats in there.

Edited June 15, 2009 by banzai510(hainz)

[Icehouse]

Vacuum advance in my experience only works with a stock carb. As long as static is around 12 and full is 32 it's good from what I understand.

[DRIVEN]

I have played with this very thing on my Mikunis. They best seat-of-the-pants solution I found is to close to what ICE said. I tuned for total advance first at 35 degrees which gave me an initial advance of about 15. My engine is bone stock and seems to run best there. It runs alright, but no better, with more advance but bumps against itself when trying to start it hot. BTW Hainz is right about the "pulsing" signal when sourcing from a single runner. As far as effect on vacuum advance, it ends up being a weak average of the pulse -- on mine about 6". There is debate on type of vacuum signal to use on advance. Most OEs use ported. Some (some Fords) use manifold vacuum. This applies full vacuum advance all the time but drops out momentarily on throttle tip-in. It essentially retards the timing under acceleration. I guess you'll just have to experiment a bit to find "best run" for your combo.

Edited June 15, 2009 by DRIVEN

[Labanon]

Some good info.

[DISLEXICDIME]

look down the carb and see what size chokes you have they might be 2 big

[slinginabullet]

i had that problem when i was running my single 45dcoe and tore the whole carb apart to find out one of the ventures in the barrel rolled just enough to block the hole on the main body of the carb from entering the venture i think you can remove the air filter use a mirror to look inside to see of the venture is at an angle like the other one is it should mirror it exactly.

[banzai510(hainz)]

MIne did that that

Venturi fell out when I took the airclearner off.

Venturi is bad as the pointy ball end wore out the venturi cup. Need a new one.

 

replace from another carb I had. all work again.

1/2 hr fix

[hang_510]

Just plug it off and run w/o?

 

since you have the requisite rising sun hood... mine run great w/o any vaccum connected.

 

 

is there any other minor vacuum leaks???

 

is it only under heavy loads (accel) that it happens?

[ggzilla]

What's the confusion? Dual-sidedrafts are primarly intended for racing, and vacuuum advance if for fuel economy. So why should the manifold or carbs have a port for advance?

 

Assuming you are using a stock-type camshaft, the vacuum advance can work. The way to do it is, drill a hole in each running, run the lines to a plenum/vacuum can (there is a formula for how big) and from the there to the distributor.

 

But why bother? It'll run OK with no bog without vacuum advance. The bog is caused by something else.

[RoadRace]

What's the confusion? Dual-sidedrafts are primarly intended for racing, and vacuuum advance if for fuel economy. So why should the manifold or carbs have a port for advance?

 

Assuming you are using a stock-type camshaft, the vacuum advance can work. The way to do it is, drill a hole in each running, run the lines to a plenum/vacuum can (there is a formula for how big) and from the there to the distributor.

 

But why bother? It'll run OK with no bog without vacuum advance. The bog is caused by something else.

 

+1

[OpelWagenGT]

What's the confusion? Dual-sidedrafts are primarly intended for racing, and vacuuum advance if for fuel economy. So why should the manifold or carbs have a port for advance?

 

Assuming you are using a stock-type camshaft, the vacuum advance can work. The way to do it is, drill a hole in each running, run the lines to a plenum/vacuum can (there is a formula for how big) and from the there to the distributor.

 

But why bother? It'll run OK with no bog without vacuum advance. The bog is caused by something else.

 

I think that sinlge side drafts are the same way and that he is right. Note exhibit A:

and I haven't seen any vaccume lines on this car, also it runs great.

Edited August 12, 2009 by OpelWagenGT